This invention relates generally to electrical power distribution equipment. More particularly, the invention relates to recloser apparatus. Still more particularly, the invention relates to a distribution class recloser employing SF.sub.6 puffer interrupters and a spring stored energy operating mechanism.
In general, a recloser is a circuit breaking or interrupting device used in the distribution of three phase electrical power. Like a circuit breaker, when a sensor or protective relay detects a fault or other system disturbance on the circuit, the recloser operates to physically separate current-carrying contacts in each phase and thereby opens the circuit and prevents the continued flow of current. A recloser differs from a circuit breaker in that a circuit breaker opens a circuit and maintains the circuit in the open position indefinitely, while a recloser operates to automatically open and reclose the circuit several times in quick succession according to a predetermined pattern. By momentarily opening and then reclosing the circuit, the recloser allows temporary faults repeated chances to clear or be cleared by subordinate protective devices. Should the fault not clear after the recloser has completed its programmed sequence of open-close operations, the recloser recognizes the condition as a permanent fault and locks the circuit open. In cooperation with the various protective relays or sensors, the recloser thus has the ability to distinguish between temporary and permanent faults on a circuit. The use of a recloser to reclose a circuit several times often prevents taking a circuit out of service when the fault or disturbance on the line was of a momentary duration only.
The major components of a recloser are the interrupters, which function to open and close the set of current carrying contacts housed therein, and the operating mechanism which, upon receipt of the appropriate control signal, provides the energy necessary to open or close the contacts. A mechanical linkage connects the interrupters and the operating mechanism.
All circuit interrupting devices can be generally classified by the type of interrupting media used to extinguish the arc that is formed as the current carrying contacts are separated, such media including air, oil, vacuum and, most recently, sulfur hexafluoride gas (SF.sub.6). To date, manufacturers have predominantly used oil or vacuum interrupters in recloser applications. The outstanding insulating and interrupting properties of SF.sub.6 gas are well known; however, the application of SF.sub.6 technology has a primarily been reserved for high-voltage applications, such as 69 KV and above, as generally it has not been economically attractive to utilize the SF.sub.6 interrupters in distribution class equipment, generally defined as 38 KV and below.
At present, the two predominate types of SF.sub.6 interrupters are the magnetic interrupter and the puffer interrupter. Magnetic type SF.sub.6 interrupters magnetically move the arc through the gas and are typically used in breaker applications where high interrupting capacities are not required. Puffer type interrupters typically use a piston to compress SF.sub.6 gas in one portion of the interrupter and then force the gas through a nozzle and across the arc so as to quickly extinguish the arc. The puffer technique is normally used in applications requiring a high interrupting capability.
Because the power distribution system typically dictates that reclosers have a high interrupting capability, if SF.sub.6 interrupters were to be employed in a recloser, it would be desirable to use a puffer interrupter. Unfortunately, compared to other interrupters, the mass of the conventional SF.sub.6 puffer interrupters requires a relatively large operating mechanism or prime mover to perform the circuit opening and closing function. For this reason, the use of SF.sub.6 puffer interrupters has primarily been limited to high voltage circuit breaker applications where the cost of the operating mechanism is a small part of the total cost of the interrupter as compared to their proportionate costs in distribution class equipment.
The requirement of a relatively large or high energy operating mechanism makes the use of a conventional SF.sub.6 puffer interrupter economically unattractive or impractical in distribution class equipment such as reclosers, despite the otherwise advantageous characteristics of SF.sub.6 gas and puffer technology. Accordingly, there is a need in the art for a recloser employing SF.sub.6 puffer interrupters that does not require the large, high energy operating mechanisms now employed on the higher voltage class equipment. Ideally, the recloser would employ SF.sub.6 puffer interrupters that are smaller, lighter and internally less complex than those of the prior art. This would lower the cost of the puffer interrupters themselves. It would also allow the use of relatively low energy operating mechanism or prime mover and thereby lower the total cost of the recloser. A smaller recloser also allows the recloser to become an integrated assembly which can be mounted in a cabinet that is fabricated from one piece of material. Further, an integrated assembly does not require assembly in sections and subsequent adjustment. Thus, costs are reduced and assembly time is saved.